What Does Hardening of Neutron Spectra Mean?

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Hardening of a neutron spectrum refers to the upward shift in average neutron energy, resulting in an increased proportion of fast neutrons and a decrease in thermal neutrons. This spectral shift can enhance the conversion of U-238 into Pu-239, facilitating greater fission production without the need for higher U-235 enrichment. Essentially, a harder spectrum indicates that neutrons are traveling at higher speeds on average. This phenomenon is significant in nuclear reactions and fuel cycle efficiency. Understanding neutron spectrum hardening is crucial for optimizing reactor performance and fuel utilization.
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Can someone explain what "hardening" of a neutron spectra means?
 
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nuclear420 said:
Can someone explain what "hardening" of a neutron spectra means?
Average neutron energy, or more particularly, the distribution of neutron energy shifts upward, or the fast neutron portion of the distribution increases while the thermal (low energy) portion of the neutron energy distribution decreases.

One can take advantage of spectral shift (shift in neutron energy spectrum) to increase the conversion of U-238 into Pu-239, which allows for more fission production without increasing the U-235 enrichment.
 
Put simply, a harder spectrum has the neutrons traveling at higher speeds (on average).
 
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